The present invention relates to a new reaction of mesityloxide with primary amines. More particularly, it relates to reaction of mesityl oxide with primary amines in admixture with other organic compounds, specifically secondary amines, to form high boiling adducts of the mesityl oxide and primary amine from which the secondary amine is readily separated in high purity.
The separation of primary amines from secondary amines is of commercial interest, but this separation is frequently complicated by their close boiling points and other physical and chemical properties. For example, piperidine (B.P. 106.degree. C.) and n-amyl amine (B.P. 104.degree. C.) are co-produced in some commercial processes. Piperidine is a valuable speciality chemical, which is commercially produced by the hydrogenation of pyridine, and sells for several dollars a kilogram. Hence, the separation and recovery of by-product piperidine would be highly beneficial. However, prior attempts to produce high purity piperidine from a mixture of piperidine and n-amyl amine have failed. The obvious approach of frictioning the by-product stream fails because the piperidine and n-amyl amine are so closely related in distillation properties that fractionation to high purity is impossible. They both form close boiling minimum azeotropes with water as well as close boiling maximum azeotropes with a number of alcohols including n-butyl, isobutyl and secondary butyl alcohol.
Several chemical reaction schemes have been proposed to separate piperidine and n-amyl amine. One process involves the reaction of the n-amyl anine with an aldehyde or ketone to form an "imine" which may be represented by the general reaction of ##STR1##
The secondary amines cannot form an imine. The reaction is reversible and the water must be removed to drive the reaction to completion. To achieve this result, high boiling ketones are employed with benzene to azeotrope the water from the reaction mixture. The piperidine can be fractionated from the reaction mixture after all of the n-amyl amine is reacted. This separation can be difficult, and this scheme is somewhat cumbersome.